In particular, the present invention relates to a double cylinder type circular knitting machine.
In such knitting machines a double ended knitting needle is used which during knitting can be transferred between the upper and lower needle cylinder assemblies. Such machines are commonly used for knitting of hosiery and/or knitwear and during each knitting cycle the selected needles will undergo various motions such as knit, miss, tuck or transfer between cylinder assemblies. These motions are imparted to the needles by sliders which have butts running along tracks in upper and lower cam assemblies associated with the upper and lower cylinder assemblies respectively.
Actuators are provided which move cam elements such as for example bolt cams in the cam assemblies for altering the path of travel followed by the butts of the sliders and thereby alter the motion undergone by the needles controlled thereby. Normally these actuators are mechanically operated from a cam drum assembly which is driven by the main drive shaft of the knitting machine via a timing transmission which normally comprises a timing chain which is indexed by a pawl mechanism.
Since a separate cam wheel is required for each actuator a large number of cam wheels have to be provided. In addition a large number of rods, cables etc. for transmitting drive from the cam followers to the components to be actuated need to be provided also. Accordingly the conventional construction of providing cam wheel assemblies for operating cam element actuators has inherent disadvantages; for example flexibility of control is restrictive since to change sequences of operation requires time consuming modification to the timing chain and/or the cam wheels. In addition the provision of a large number of mechanical components around the upper and lower cylinder assemblies not only restricts access to the cylinders and associated cam assemblies but also imposes the need to continually lubricate and/or service the mechanical linkages.
An advantage of using a cam drum assembly for operating cam elements is that positive positional control under adequate power is provided for moving the cam element into and out of cam tracks in the cam assemblies. This is particularly so for cam elements which need to be accurately located a several distinct positions when being inserted into or retracted from a cam track. For instance in the cam assembly associated with the lower cylinder of a double cylinder circular knitting machine adapted for knitting half hose having a heel pouch it is necessary for a cam element to be positioned at 4 discrete positions, viz a fully retracted position whereat it does not co-operate with butts on any needle slider, a fully inserted position whereat it co-operates with butts on all needle sliders and two intermediate positions whereat it co-operates with butts of selected needle sliders having a predetermined butt height.
In view of this multi-stage positioning and power capability provided by actuators operated by a cam wheel assembly such assemblies have remained in common usage despite the disadvantages exemplified above.